A.7,5,1,3 B.7,3,1,5 C.5,1,3,7 D.7,5,3,1
A.e=f->data;r=r->next B.e=f->data;r->next=r C.e=f->data;f=f->next D.e=f->data;f->next=f
A.16,12,8,4 B.4,8,12,16 C.8,4,16,12 D.16,12,4,8